1. Field of the Invention
This invention relates in general to magnetic recording apparatus and, in particular, to apparatus for use in the playback of information recorded on a magnetic disc.
2. Description Relative to the Prior Art
It is well known in the field of magnetic recording to employ what are called equalization circuits. Equalization, as employed in the playback of magnetically recorded information, serves to correct playback inequities which stem from the fact that playback signal processing is, in general, frequency dependent: With a typical inductive playback head that is dependent on recorded signal flux rate of change, the playback voltage-versus-log frequency response curve rises with frequency, only to fall off eventually as the playback wavelength approaches the gap length of the playback magnetic head. Further, because the inductive reactance of the aforenoted head is frequency dependent (i.e. X.sub.L =2.pi.fL), differing signal delays inherently become associated with the various signal components which comprise, say, a recorded pulse that is played back by means of such head; these differing signal delays manifest themselves as phase disparities among the various signal components which comprise the played back pulse. To effect a flattened, or otherwise shaped, voltage-versus-log frequency curve, amplitude equalization is employed, whereby (typically) lower and higher signal frequencies receive more gain than mid-range signal frequencies; to bring the various signal frequency components which comprise a played back signal into proper phase relationship with respect to each other, frequency dependent phase equalization is employed.
In variable speed magnetic tape recorders, it is known to vary the degree of equalization as a function of tape speed: At one tape speed, the equalization would be set one way; at any other tape speed, the equalization would be set another way. Lowman, in his text "Magnetic Recording", McGraw-Hill Book Company, pg. 178, describes such a variable equalization circuit in which "speed gates" select one or another pair of gain and time delay circuits, depending on which of six recorder tape speeds is employed.
Currently, there appears in the literature various disclosures for an electronic still camera in which a magnetic disc is spun at relatively high speed in relation to a record head within the camera. As each picture is "snapped", an encoded video signal is recorded in a respective (or grouping of) circular track(s) about the rotary axis of the disc. The disc, therefore, ultimately comprises a plurality of recorded tracks . . . and these, incidentally, reside in a relatively narrow band around the disc. Typically, there would be upwards of eighty video tracks per disc. During playback of video information recorded on such a disc, a playback head is positioned respective of the track whose encoded picture is to be displayed. (While the invention, as will appear below, is cast in the environment of an 80-track "video" disc, it is not so limited and may, if appropriate, be accommodated to digital and other forms of analog recording.)
Other art which may be germane to the present invention may be found in:
______________________________________ U.S. Pat. No. Title Date ______________________________________ 2,247,924 Automatic Equalizing Sys- 7/1/41 tem For Recording On Disk Records 3,430,215 Automatic Gain Level 2/25/69 Stepping System 3,944,754 Record Disc Recording Sys- 3/16/76 tem With Signal Amplitude Controlled By Stylus Arm Position 4,170,022 Apparatus And Process For 10/2/79 Recording With Variable Correction Of A Television Signal Having Three Com- ponents ______________________________________